Multiple layered strippable adhesive tapes for sealing carton flaps for joints during manufacture or after being filled are well known in the art. Various types of these tapes have been developed over the years to meet different applications and satisfy different requirements in sealing. Indeed, applicant is the inventor of one such tape disclosed and claimed in U.S. Pat. No. 4,041,202 issued Aug. 9, 1977, incorporated herein by reference. That invention solved many problems in the prior art and provided a delaminatable tape which could be stripped away to leave two lateral portions of a bottom layer separated on the two sides of a joint to thereby release the pieces being joined.
Generally in the prior art these multiple layered tapes have reinforcing fibers, perhaps made of fiberglass or the like, extending laterally across the tape to increase its strength. This type of construction results in a somewhat rough and uneven surface along both the top and bottom of the tape, as well as a somewhat thicker tape. Not only does this decrease the flexibility of the tape as the reinforcing fibers resist any folding or twisting of the tape from its flattened orientation, but it also increases the diameter of a roll of tape as the uneven surfaces do not closely wrap atop each other. Furthermore, the relative inflexibility and uneven surfaces reduce the effectiveness of the tape in adhering to the roughened surface of a carboard box or carton as the tape is less able to conform to the surface of the carton and instead exerts a tension against the adhesive tending to return the tape to its original orientation and separate it from the carton surface, which may itself be rough and uneven. Of course, the compound structure involving the use of fiberglass twine and high strength Kraft paper or the like makes for a high strength tape capable of withstanding much higher stress and loading, but it also represents a significantly higher cost factor than that of simple Kraft paper tape.
Plastic tapes are also known in the prior art and provide many advantages when used as the strength layer in a delaminatable tape as mentioned above. However, an inherent problem with using plastic is that it cannot hold a water soluble adhesive. Furthermore, a rather thin film of plastic may be used as the strength layer to achieve the same characteristics of much thicker prior art tapes, but this thinness becomes a disadvantage in that it prevents its being dispensed by standard Kraft paper tape dispensing machines which rely upon the longitudinal stiffness of the tape to unwind it from the roll and force it through the dispenser. Of course, most Kraft paper type dispensers also have a water reservoir or the like which moistens the adhesive surface of the tape and ready it for application. Thus, a water soluble adhesive is virtually a necessity as well.
Accordingly, applicant has combined the advantages of a plastic strength layer in a delaminatable tape by utilizing a relatively thin carrier layer of Kraft paper or the like which is coated with a water soluble adhesive and provides sufficient rigidity to the tape so that it can be dispensed from the standard Kraft paper type tape dispenser. As the plastic film provides the necessary strength, the carrier layer need only be sufficiently thick to provide the minimum rigidity required to "stiffen up" the tape for dispensing. Thus, a significant reduction in thickness can be achieved with plastic as the strength layer. No minimum thickness is required to satisfy the function of "carrying" the water soluble adhesive as the lamination between the carrier layer and the strength layer can be sufficiently strong to anchor them in place and help prevent the disintegration of the carrier.
As can be appreciated, the plastic film is substantially thinner, smoother, and thus results in much greater flexibility and bonding between the tape and the carton surface. Furthermore, a thin layer of plastic provides much greater strength than the construction of prior art tapes. By pre-stretching and orienting the strength layer of the tape, inadvertent and undesired separation of the strength layer from the carrier layer due to their different flexibilities is avoided. This also reduces the tension on the lamination between the two layers and helps maintain its integrity as the pieces of the carton joined by the tape move and flex in response to its use.
All of the inherent advantages provided by a plastic tape having a water soluble adhesive and sufficient rigidity for dispensing are available in a strippable tape with applicant's invention. These include the ability to manufacture the tape at much greater speed than prior art constructions as the fiberglass threads are eliminated from its construction. The cost is significantly reduced because of its relative simplicity of construction and utilization of fewer and less expensive materials. The plastic, which may be any polymer or co-polymer, is much more flexible than prior multiple layer constructions and adheres much better to the carton or the like. As the tape is substantially thinner, and also provides a smooth flattened surface across its width, it may be wound with much greater efficiency into rolls such that approximately twice as much of applicant's tape can fit within the space required by the prior art fiberglass reinforced tape.
In applicant's preferred embodiment, the carrier layer may be made of a thin low internal bond Kraft which partially separates internally with the stripping of the upper strength layer so that any carrier layer that remains on the carton is so weak that it may be easily broken to permit opening of the carton. While the invention may also employ a medial slit cut into the carrier layer which would form a line of separation as the upper strength layer is stripped from the tape, this is not necessary and is only a matter of choice.
Applicant's tape is described herein in connection with its use in either manufacturing or closing cardboard cartons. However, it is to be understood that such use is only one of many types of uses suitable for applicant's tape and is not to be considered a limiting feature thereof. Some of the unique features and advantages of applicant's tape have been described above. Further and more detailed explanation leading to a more complete understanding of applicant's invention may be had by reviewing the drawing and preferred embodiment which follows.